1. Field of the Invention
The present invention relates to magnetic sensing elements mainly used for magnetic sensors, hard disk drives, etc., and to methods for fabricating the same. More particularly, the invention relates to a magnetic sensing element which is suitable for track narrowing and which has improved magnetic sensitivity, and to a method for fabricating the same.
2. Description of the Related Art
FIG. 17 is a sectional view which shows a structure of a conventional magnetic sensing element, viewed from the surface facing a recording medium.
The magnetic sensing element shown in FIG. 17 is a spin-valve thin-film magnetic sensing element which is one type of giant magnetoresistive (GMR) element using a giant magnetoresistance effect, and it detects a recorded magnetic field from a magnetic recording medium, such as a hard disk.
The spin-valve thin-film magnetic sensing element includes a multilayer film 9 in which a substrate 8, a first antiferromagnetic layer 1, a pinned magnetic layer 2, a nonmagnetic material layer 3, and a free magnetic layer 4 are deposited in that order from the bottom; a pair of second antiferromagnetic layers 6 formed on the multilayer film 9; and a pair of electrode layers 7 formed on the second antiferromagnetic layers 6.
Typically, the first antiferromagnetic layer 1 and the second antiferromagnetic layers 6 are composed of Fe—Mn alloy films, Ni—Mn alloy films, or Pt—Mn alloy films; the pinned magnetic layer 2 and the free magnetic layer 4 are composed of Ni—Fe alloy films; the nonmagnetic material layer 3 is composed of a Cu film; and the electrode layers 7 are composed of Cr films.
Preferably, the magnetization of the pinned magnetic layer 2 is aligned in a single domain state in the Y direction (the direction of a leakage magnetic field from the recording medium, i.e., in the height direction) by an exchange anisotropic magnetic field with the first antiferromagnetic layer 1, and the magnetization of the free magnetic layer 4 is aligned in the X direction by exchange anisotropic magnetic fields from the second antiferromagnetic layers 6.
That is, preferably, the magnetization direction of the pinned magnetic layer 2 is substantially perpendicular to the magnetization direction of the free magnetic layer 4.
In the spin-valve magnetic sensing element, a sensing current is applied from one of the electrode layers 7 formed on the second antiferromagnetic layers 6 to the free magnetic layer 4, the nonmagnetic material layer 3, and the pinned magnetic layer 2. The recording medium, such as a hard disk, travels in the Z direction. When a leakage magnetic field is applied in the Y direction from the recording medium, the magnetization direction of the free magnetic layer 4 is changed from the X direction to the Y direction. Electrical resistance changes due to the relationship between the varying magnetization direction of the free magnetic layer 4 and the pinned magnetization direction of the pinned magnetic layer 2, which is referred to as the magnetoresistance effect, and the leakage magnetic field from the magnetic recording medium is detected by a voltage change based on the change in the electrical resistance.
In order to fabricate the spin-valve magnetic sensing element shown in FIG. 17, after the multilayer film 9 is formed, a resist layer R for a lift-off process is formed on the multilayer film 9 as shown in FIG. 18, and the second antiferromagnetic layers 6 and the electrode layers 7 are formed by ion beam sputtering or the like. Layers 6a having the same composition as that of the second antiferromagnetic layers 6, and layers 7a having the same composition as that of the electrode layers 7 are formed on the resist layer R.
Sputtered particles are not easily deposited on the regions covered by both ends of the resist layer R. Therefore, in the vicinities of the regions covered by the ends of the resist layer R, the thicknesses of the second antiferromagnetic layers 6 and the electrode layers 7 are small, and as shown in FIGS. 17 and 18, the thicknesses of the second antiferromagnetic layers 6 and the electrode layers 7 decrease in the side regions sandwiching the track.
Consequently, the effect of the exchange coupling magnetic field between the free magnetic layer 4 and the second antiferromagnetic layer 6 at each side region S is decreased. As a result, the magnetization direction of the free magnetic layer 4 in the side region S is not completely pinned in the X direction, and when an external magnetic field is applied, the magnetization direction of the free magnetic layer 4 is varied.
In particular, when the track is narrowed in order to improve the recording density in the magnetic recording medium, side reading may occur in which, in addition to information in the magnetic recording track to be read within the track width Tw region, information in the adjoining magnetic recording tracks is also read in the side regions S.
In the structure in which the second antiferromagnetic layers 6 are deposited on both sides in the track width direction of the free magnetic layer 4, the central region in the track width direction of the free magnetic layer 4 tends to be insufficiently aligned in a single domain state and the magnetization direction tends to be insufficiently controlled.
Consequently, instead of the structure of the magnetic sensing element shown in FIG. 17 in which the second antiferromagnetic layers 6 are deposited on both sides of the free magnetic layer 4 with a distance corresponding to the track width therebetween, a structure has been devised in which, as shown in FIG. 19, by depositing a second antiferromagnetic layer 10 on the entire upper surface of a free magnetic layer 4, the region corresponding to the track width Tw of the free magnetic layer 4 is aligned in a single domain state, and the magnetization is directed substantially perpendicular to the magnetization direction of a pinned magnetic layer 2.
In order to align the region corresponding to the track width Tw of the free magnetic layer 4 in a single domain state and direct the magnetization substantially perpendicular to the magnetization direction of the pinned magnetic layer 2, the exchange coupling magnetic field between the free magnetic layer 4 and the second antiferromagnetic layer 10 must be increased. If the exchange coupling magnetic field is excessively increased, the magnetization of the free magnetic layer 4 is not varied when a leakage magnetic field from the recording medium is applied in the Y direction, and magnetic sensitivity is lost.
In the structure shown in FIG. 19, it is very difficult to adjust the magnitude of the exchange coupling magnetic field between the free magnetic layer 4 and the antiferromagnetic layer 10 so that the magnetization direction of the free magnetic layer 4 is substantially perpendicular to the magnetization direction of the pinned magnetic layer 2 and the magnetization direction of the free magnetic layer 4 is varied by the leakage magnetic field. The structure shown in FIG. 19 is thus impractical.